NASA / Blue Marble ProjectIf you step outside anywhere on the surface of the Earth, there's no obvious signs that tell you the Earth isn't flat. And if you add a little bit of math in there, you won't simply discover that the Earth is round, you'll actually be able to measure how big it is for yourself. If you started out level with that buoy, you'd be able to see it in its entirety, no problem. Nick Page / flickrJust observing how this happens should be able to prove that the Earth is round. But we can go farther, and set up an experiment to actually measure the physical size of the Earth based on these observations.

Source: Forbes March 28, 2017 13:52 UTC